Global climate change is frequently considered a major conservation threat. The Earth's climate has already warmed by 0.5 Њ C over the past century, and recent studies show that it is possible to detect the effects of a changing climate on ecological systems. This suggests that global change may be a current and future conservation threat. Changes in recent decades are apparent at all levels of ecological organization: population and life-history changes, shifts in geographic range, changes in species composition of communities, and changes in the structure and functioning of ecosystems. These ecological effects can be linked to recent population declines and to both local and global extinctions of species. Although it is impossible to prove that climate change is the cause of these ecological effects, these findings have important implications for conservation biology. It is no longer safe to assume that all of a species' historic range remains suitable. In drawing attention to the importance of climate change as a current threat to species, these studies emphasize the need for current conservation efforts to consider climate change in both in situ conservation and reintroduction efforts. Additional threats will emerge as climate continues to change, especially as climate interacts with other stressors such as habitat fragmentation. These studies can contribute to preparations for future challenges by providing valuable input to models and direct examples of how species respond to climate change. Consecuencias Biológicas de Cambios Climáticos RecientesResumen: El cambio climático global es frecuentemente considerado como una gran amenaza para la conservación. Sin embargo, el clima de la tierra ya se ha calentado 0.5 Њ C a lo largo del siglo pasado y estudios recientes muestran que es posible detectar los efectos de un clima cambiante en los sistemas ecológicos. Esto sugiere que el cambio global puede ser una amenaza presente y futura para la conservación. Los cambios en las décadas recientes son aparentes a todos los niveles de organización ecológica: cambios poblacionales y de historia de vida, sesgos en el rango geográfico, cambios en la composición de especies en comunidades y cambios en la estructura y funcionamiento de ecosistemas. Estos efectos ecológicos pueden estar ligados a disminuciones poblacionales recientes y a la extinción de especies tanto en el ámbito local como global. A pesar de que es imposible probar que el cambio climático es la causa de estos efectos ecológicos, estos estudios tienen implicaciones importantes para la biología de la conservación. Ya no es seguro asumir que todo el rango histórico de una especie permanece apto. Al llamar la atención sobre la importancia del cambio climático como una amenaza actual para las especies, estos estudios hacen énfasis en la necesidad de esfuerzos de conservación contemporáneos que tomen en consideración el cambio climático tanto para esfuerzos de conservación in situ, como de reintroducción. Emergerán amenazas adicionales en tanto el clima continúe...

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Unpredictable, short‐term changes in environmental conditions associated with weather patterns have severe impacts on the reproductive success of Tree Swallows Tachycineta bicolor, as well as other aerial insectivores. We examined the effects of day‐to‐day environmental variation on the growth of nestling Tree Swallows. Using path analysis, we compared the relative importance of changes in food availability, ambient temperature and wind speed on changes in mass and feather length over four years at our study site near Ithaca, New York. Changes in environmental conditions explained a significant amount of the variation in nestling growth, with daily high temperature having the greatest influence for nestlings younger than five days. Both food supply and temperature had significant direct effects on growth of nestlings older than nine days, with temperature also having a significant indirect effect through its influence on food availability. For both young and old chicks, mass gains were smaller for chicks hatched later in the season. Environmental conditions also explained a significant amount of the linear growth of the ninth primary feather in one of two years, with food supply showing the most consistent positive effect. Environmental conditions several days prior to the measurements significantly influenced feather growth, indicating that the effects of adverse conditions are spread out over several days of feather growth, but this effect was not seen for change in mass.